The overall goal is to determine how psychological processes interact with physiology to influence the occurrence of physiological responses, the patient's perception that these physiological responses represent symptoms of disease, and his/her decision to seek health care. Studies are proposed in four areas: (1) Validation of diagnostic criteria for functional GI disorders. The validity of diagnostic criteria for all functional GI disorders recommended by an international commission will be tested by (a) administering a validated Gi symptom questionnaire to 1,876 general medical patients, (b) using principal components factor analysis to empirically define functional GI disorders as groups of symptoms which covary across individuals, (3) comparing the published criteria which are based on the consensus of experts to the empirically derived criteria, and (d) comparing both the consensus criteria and the empirically derived criteria to the judgments of experienced clinicians. (2) Determinants of illness behavior. A multicenter study of 500 patients with functional bowel disorders will compare cognitive behavior therapy, interpersonal psychotherapy, and a tricyclic antidepressant to placebo. Pain thresholds and rectal motility, in addition to psychiatric diagnosis and psychological distress, will be assessed before and at the end of treatment to assess the relative contribution of altered physiology and psychological variables to symptoms and to symptom improvement with treatment. (3) Psychophysiology of irritable bowel syndrome (defined by abdominal pain associated with altered bowel habits). In Study I, CNS influences on pain perception will be investigated by comparing irritable bowel patients and controls with respect to sensitivity and response bias when discriminating between two intensities of painful stimulation in a signal detection paradigm. Half of the 30 female irritable bowel patients and half of the 30 control women will have been sexually abused. In Study II, pain thresholds will be tested throughout the colon in irritable bowel patients an controls to identify areas of increased sensitivity. In Study III, rectal biopsies from irritable bowel patients who show increased sensitivity to distension stimuli and from controls will be analyzed for cytokines and gastrointestinal peptides to identify possible mechanisms for increased pain sensitivity in irritable bowel syndrome. (4) Constipation in the Elderly. In Study I, young and old clinic patients will be compared to determine which physiological subtypes of constipation are more common in the elderly. In Study II, the relationship of constipation to age, diet, exercise, and psychological traits will be investigated in the Baltimore Longitude Study on Aging (1,035 participants stratified by age). Subjects who have not consulted physicians about their constipation will be matched to clinic patients to investigate how psychological traits influence health care utilization. In Study III, biofeedback training to teach relaxation of the pelvic floor muscles will be compared to progressive muscle relaxation training and to a high fiber diet in the treatment of pelvic floor dyssynergia, a specific type of constipation.